This invention relates to three dimensional, periodic absorption, phase change dispersing lenses having a near-unity intensity ratio for maximal laser dispersion.
In U.S. Pat. No. 5,831,769, a lens includes a medium which absorbs laser radiation that may be harmful to the eye or other high gain optics, raising its temperature and thereby changing its index of refraction in a pattern, which causes a phase change in the radiation passing therethrough. The medium may be periodically bounded by thermal sinks, thereby providing a periodic differential in temperature rise, may be provided in a length of absorption material which varies periodically or may have a density of absorption material which varies periodically, thereby to have a periodic absorption characteristic. The periodicity, which may be regular or random, provides a periodic variation in total phase change, which causes interference (thermal blooming) that disperses the radiation sufficiently to lower the intensity at the retinal spot, or other light-responsive surface, to a level below that which would cause damage. Eyeglasses with mutually perpendicular periodicity provide degraded vision of useful images while being protected from harmful radiation.
It has been determined that the foregoing laser protection lens is not as effective as possible, particularly per unit of axial thickness of the lens (parallel to the path of radiation to the eyes or instruments being protected thereby).
Objects of the invention include provision of laser protection lenses having the capability to reduce the intensity of received laser radiation at the focal plane (the retina or other light responsive surface) by an amount which is 10,000 times greater than the reduction of intensity to other radiation, particularly useful radiation, passing through the lens; laser protection lenses having laser dispersing characteristics many orders of magnitude greater than those heretofore attainable; laser protection lenses which are extremely effective, capable of protecting against incoming radiation of many tens of milliwatts per square centimeter while having a thickness of only several millimeters; and laser protection lenses capable of protecting against a plurality of distinct frequency bands of laser radiation.
According to the present invention, a lens for protecting optical systems having high optical gain, such as the human eye and optical instruments of high optical gain, induces thermal blooming of laser radiation passing therethrough by means of phase distortion created by a spatially-varying absorption or reflection characteristic.
In accordance with the invention, the disparity in absorption or reflection may be two dimensional (as in said patent) or may be three dimensional, as shown hereinafter.
According further to the present invention, the segments of varying absorption may take the form of a first section absorbing laser radiation of one or a plurality of frequency bands, and a second section having a plurality of groups of volumes, at least one group absorbing laser radiation of a first band of frequencies, and a second group of volumes not absorbing laser radiation of said first band; the second group may absorb no laser radiation, or may absorb laser radiation of a different frequency band. The second group of volumes may totally surround each volume in the first group, or the first and second volumes may be arranged in a matrix. In still further accord with the invention, there may be three different volumes, each absorbing laser radiation of a different band of frequencies; or, there may be two groups of volumes in one section adjacent the optical entry surface and two groups of volumes in another section adjacent said one section. According to the invention further, the groups of volumes may be arranged in a regular or irregular two-dimensional matrix.
In accordance with the invention, the second volumes, within the second section, may simply comprise strips disposed on an optical entry surface of the first section of a lens. In still further accordance with the invention, the strips may either be an absorption material, such as lead glass, or a reflecting material, such as a dielectric reflector formed in a suitable pattern by vapor deposition, by nanotechnology, or otherwise, directly on the optical entry surface of the first section.
An important aspect of the present invention is the potential to utilize vapor deposited reflecting elements, which may be quite thin, and have low weight. Such elements are easily made in virtually any pattern which can be achieved by low cost, conventional vapor deposition techniques.
According to the invention further, the various volumes for absorbing one or more bands of frequencies are formed of lead glass, so as to take advantage of a very high temperature coefficient of change of the index of refraction, thereby to achieve maximal phase difference and commensurate interference.
In accordance further with the invention, the absorption material may be submicron particles, or it may be a suitable dye.
Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.